Engine starter



Nov. 21, 1950 s. GILBERT 2,530,869

ENGINE STARTER Filed Feb. 25, 1949 v INVENTEJIET SAMUEL G/LB 3 BY 1 K APatented Nov. 21, 1 950 UNITED STATES PATENT OFFICE ENGINE STARTERSamuel Gilbert, Cedar Grove, N. J., assignor to Bendix AviationCorporation, Teterboro, N. J., a corporation of Delaware ApplicationFebruary 25, 1949, Serial No. 78,380

1 Claim. 1

The present invention relates to starters and more particularly todirect cranking starters for gas high speed engines such as gas turbinesfor aircraft.

In starters of this type, the starter motor drives the aircraft turbinedirectly and they are usually provided with a preset torque limitingclutch for protecting the starter mechanism should the engine abnormallyresist cranking. This torque limiting clutch, however, does not protectthe starter mechanism against shock-loading at the moment the crankingpower is applied, and the instantaneous shock-loading, particularly onthe starter jaw and the jaw advancing mechanism, may reach valuesgreatly exceeding the preset torque limiting value of the frictionclutch. Various means and methods such as the use of additional frictionclutches with adjustable friction characteristics have been proposed toreduce the initial shock-loading and yet have sufficient torquetransmitting capacity after engagement of the starter jaw with theengine to transmit the torque necessary to crank it. However, it hasbeen found that ordinary friction type slip clutches are not suitablefor absorbing the mentioned shock loading in starters operating at veryhigh speeds for use with modern high speed aircraft engines such as gasturbines, because of the tendency of this type of clutch to score orburn up under rapid surface slipping. These problems are becoming acuteas the size and starting speed of the aircraft engines are increased,entailing the use of rapidly accelerating high power starter motors suchas motors driven by gases released under extremely high pressures.

Accordingly, one object of the present invention is to provide a novelcombination in an engine starter whereby a high speed, high powerstarter motor may be utilized.

Another object of the present invention. is to provide a novelcombination in a starter whereby the starter may be made of small sizeand light weight, yet capable of transmitting large amounts of startingpower at rapid acceleration rate and having torque limitingcharacteristics variable with the speed of the starter.

A further object is to provide a novel combination in an engine starterwhereby a standard starter jaw and jaw advancing and driving mechanismmay be utilized to crank an engine requiring high speed cranking andhigh initial turning torque.

The above and other objects and features of the invention will appearmore fully hereinafter from a consideration of the following d$ P- tiontaken in connection with the accompanying drawing wherein the singlefigure of the drawing shows a portion of the starter, partly in sectionand partly in elevation, illustrating one embodiment of the presentinvention by way of example. The starter motor (not shown) may be anelectric motor or a motor driven by steam, compressed air or gasesresulting from combustion or other chemical action, and is connected toan output member Ill journaled within a transverse member or wallportion 12 of starter housing M as by ball bearing H5. The drivingmember I0 is adapted to drive a starter jaw advancing and drivingmechanism generally indicated at i6 and including an actuating nut I?through a fluid or hydraulic coupling [8 and a planetary drive 26. Thefluid coupling is shown as comprising an inner rotatable driving memberor impeller 22 mounted on a stub shaft 24 whose one end is rigidlyconnected to the motor output member in and Whose other end is journaledclosely adjacent and coupled through a fluid to the driven couplingmember or runner 26 having a hub portion 28 carrying a pinion 30 andjournaled in bearing 32 within flanged end portion 3| of actuating nutH. The other end of the stub shaft 24 is journaled in the hub portion28. The fluid or hydraulic coupling l8 may be of a type well known inthe art and a detailed description thereof is not deemed necessary.

Fluid coupling output pinion 30 is shown as driving a planetaryreduction gearing 20 having one or more planet gears 34 meshing withstationary orbit gear 38 and journaled on trunnions 36 shown as integralextensions of end portion 3| of actuating nut 1''. Nut I1 is journaledby a pair of roller bearings M! in housing l4 and adapted to engageexternally threaded screw shaft 42 which carries and is splined tostarter jaw member 44. A baffle plate 46 secured to mounting flange 41of starter housing [4 supports a friction split ring 48 surrounding, andin frictional engagement with, jaw 44 in retracted position, and alsosupports a seal ring 49 adapted to prevent oil or other fluid fromentering the starter from the engine to be started. The seal ring may beomitted if roller bearings 40 are replaced by sealed ball bearings.

When the motor is energized, the motor output member will rotate nut llthrough the fluid coupling l8 and planetary gearing 20. Rotation of nutI! will force screw shaft to the left as viewed in the drawing becausethe shaft will be restrained from rotating by the action of the I GfiOnplitring 48 against starter jawmemher 44. When the starter jaw is infull engagement with engine jaw 45 a shoulder 50 on the screw shaft 42will abut a corresponding shoulder 52 on the nut whereupon furtherrotation of the nut will rotate the screw shaft and thereby crank theengine. It will be noted that the friction slip ring will have riddenoff ramp 54 on the starter jaw 44% when the latter hasengaged engine jaw45 and will not hinder the free rotation of the screw shaft and starterjaw.

The jaw advancing mechanism per se comprising nut screw shaft 42 and jaw44-is-well known to those skilled in the art, but heretofore this jawadvancing mechanism has been operated by a barrel surrounding the nutand splined thereto by a disc pack having discs alternately splined tothe barrel and thenut and having a preset torque limiting valuesufficiently high to insure cranking of the engine. With the use of highspeed rapidly accelerating motors the shock and impact loading. on. thestarter and engine jaws44 and 45, respectively, screw shaft 42 and nutI? will. reach. instantaneous values greatly exceeding the preset torquelimiting value of the disc pack because of. the high static frictionthereof. By the use of the fluid coupling in com-' bination with thisjaw advancing mechanism, the starter jaw will moveinto engagement withthe-engine jaw at a very slow rate compared to the rate which wouldhaveresulted had the motor been connected to the jaw advancing mechanismthrough a preset clutch having a relatively-high torque limiting. value.The torque limiting characteristics of a fluid coupling are extremelyfavorableunder these conditions because at'low drive speeds, e. g. whenthe jaw engagement takes place and the initial cranking occurs, thetorque limit is relatively low so as to protectthe starter mechanism byslippage should theengine to be started abnormally resist initialcranking;

As the cranking speedincreases the torque limiting: value of the fluidcoupling increases up to a predeterminedlimit determined, by thedesignthereof and the particular fluid employed. Thus; during thecranking operation this novel combination providesinitially maximumprotection when the danger of damage is greatest and then graduallybrings about the application of increased torque suificient to start anengine under even the most adverse weather conditions. The total absenceof shock loading makes it possible to decrease the size of the operatingparts of the starter and will eliminate shock failure-of starter. andengine parts which is extremely important for efficient operation of theaircraft.

Although only one embodiment of the invention has been illustrated anddescribed, various changes in the form and relative arrangements of theparts may be made to suit requirements.

What is claimed is:

An engine starter comprising, in combination, astarter motor of arapidly accelerating high speed type, a jaw advancing mechanismcomprising a rotatable internally threaded nut, an externally threadedscrew shaft concentrically arranged within-said nut having threadsadapted toengage the threads of said nut and having connected thereto astarter jaw, a fluid-coupling including an impeller and a runner, saidrunner having a hub portion rotatably'supportedby'said nut, saidimpeller havinga stubshaft one end of which is rigidly' connected to thestarter motor and the other end of which is journaled in the hubportion, a planetary reduction gearing drivingly connecting said hubportion to said nut, said screw shaft beingaxially movable upon rotationof said nut to move said starter jaw into engagement with-a mating jawmember of the engine to be started and then to rotate with said nut tocrank the engine to be started.

SAMUEL GILBERT.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Ayres Dec. 7, 1937

